Do not try to shallow git history when the protocol doesn't allow it.

This only happens with the old git http dumb protocol, but that's what we use in our integration tests.
We check the Content-Type header advertised in http requests to make sure the http transport is the git smart transport:

See this commit as a reference:
https://github.com/git/git/commit/4656bf47fca857df51b5d6f4b7b052192b3b2317

Signed-off-by: David Calavera <david.calavera@gmail.com>

builder/job.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"net/http"
 	"os"
 	"os/exec"
 	"strings"
@@ -114,7 +115,9 @@ func Build(d *daemon.Daemon, buildConfig *Config) error {
 		}
 		defer os.RemoveAll(root)
 
-		if output, err := exec.Command("git", "clone", "--depth", "1", "--recursive", buildConfig.RemoteURL, root).CombinedOutput(); err != nil {
+		clone := cloneArgs(buildConfig.RemoteURL, root)
+
+		if output, err := exec.Command("git", clone...).CombinedOutput(); err != nil {
 			return fmt.Errorf("Error trying to use git: %s (%s)", err, output)
 		}
 
@@ -239,3 +242,21 @@ func Commit(d *daemon.Daemon, name string, c *daemon.ContainerCommitConfig) (str
 
 	return img.ID, nil
 }
+
+func cloneArgs(remoteURL, root string) []string {
+	args := []string{"clone", "--recursive"}
+	shallow := true
+
+	if strings.HasPrefix(remoteURL, "http") {
+		res, err := http.Head(fmt.Sprintf("%s/info/refs?service=git-upload-pack", remoteURL))
+		if err != nil || res.Header.Get("Content-Type") != "application/x-git-upload-pack-advertisement" {
+			shallow = false
+		}
+	}
+
+	if shallow {
+		args = append(args, "--depth", "1")
+	}
+
+	return append(args, remoteURL, root)
+}